Ultra high frequency oscillator



Feb. 24, l.

J. A. MOTON ULTRA lHIGH FREQUENCY OSCILLATOR Filed Aug. 8, 1942 f5) 2S eM5 3 Jl l l llll l Il 22 2a 2s r /f u ullnlglslellm 2/ ollllllullllllllllllll 0R TON Patented Feb. 24, 1948 ULTRA HIGH FREQUENCYOSCILLATOR .lack A. Morton, Warren Township, Somerset County. N. J..assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y.,a corporation of New Yorls Application August 8, 1942, Serial No.454,112

This invention relates to electronic devices for the production of highfrequency electrical energy and particularly to such devicescharacterized by the use of hollow closed resonators and in whichelectron transit time is a factor of importance.

An object of the invention is to provide an efflcient oscillator capableof operation at high frequencies with relatively low direct currentpower supply voltages.

Another object is to provide such an oscillator incorporating theadvantages o f closed completely shielded high frequency circuits.

Another object is to provide such an oscillator of which the frequencyis conveniently adjustable.

Another object is to provide such an oscillator which is relativelycompact.

.Another object is to provide such an oscillator having good frequencystability.

Resonant cavity type oscillators oii'er many ad vantages when energy atvery high frequencies. is

to be generated. Such oscillators may employ ar f single cavity or anumber of cavities and many. diiierent methods o f operation may beemployed. For example, a familiar type employing two cavity resonatorsutilizes the first cavity to vary the velocities of the electrons in anelectron stream, a drift space between the two resonators to allow theaccelerated electrons to overtake decelerated electrons thus producingdensity varia tions in the stream and a second resonator to be excitedelectrically by the density varied stream. The device of the presentinvention differs from this and other well-known resonant cavityoseillators in several respects while incorporating the advantages ofthe cavity resonator type of circuit.

A resonant cavity type of circuit is employed and through a portion ofthe high frequency field associated with that cavity when it isenergized is directed a stream oi' electrons from a cathode. By suitableelectrodes and biasing potentials applied thereto' a direct currentelectric field is superposed' upon the portion of the high frequencyfield traversed by the electron stream such that it opposes the iiow ofelectrons tending to return them toward the cathode. Adjustments may bemade so that `electrons entering the high frequency field in such" phaseas to absorb energy and be accelerated will overcome the retardation ofthe direct current field and pass on through while electrons entering insuch phase as to give up energy to the high frequency field and be de'celerated will not be able to overcome the re. tardation of the directcurrent eld and so will be and a dinthsoppoeite 14 Cl. (Cl. 315-6)rection. again giving up energy to the high irequency field. Thus, sincethe energy giving electrons traverse the ileld twice while the energyabsorbing electrons traverse the field only once the energycontributions preponderate and high irequency oscillations are sustainedin the cavity resonator circuit. The output and eiilciency of the deviceare enhanced by utilizing a resonant cavity input circuit energized byfeedbackl from the output circuit to control the space charge current ina manner to eliminate from the electron stream the energy absorbingelectrons which as explained above traverse the high frequency fieldonly once and absorb A high frequency energy rather than contribute toit.

The invention will be described more fully by k\`\ output circuit acavity input circuit with a feedtance across the annular space betweenmembers t the size of back circuit to energize it whereby the electronstream is modulated at the operating frequency and the elciency ofoperation enhanced, and Fig. 3 shows a modiilcation ol the Fig. 2 devicein which the oscillations are produced initially in the cavity inputcircuit which is electron coupled to the output circuit, half of theelectrons exciting the input circuit and the other half exciting theoutput circuit.

'leferring now to Fis. l, an insulating evacuatedi envelope i containsthe indirectly heated cathode 2. the grid electrodes 3 and t and theplate electrode 5, all of these being supported by and connected to thedisc members 22, 23, 2t and 2d, respectively, which are fused into'theenvelope l and serve to connect the electrodes to external circuits.'I'he cavity resonator 2l is con- `;-venlent1y made in coaxial form asshown and is bounded by members t, di. il, i2, it, it, it and d. Thisresonator is the sole high frequency cir cuit of the oscillator properin Fis. l. The an nular members i2 and it are spaced ra from each otherto provide direct current insula tion between electrodes d and but thecapaci'- lt and It is made sufficiently large to provide a low impedancehigh frequency path thus effectively closing the resonator between thecoamal members it and il. Members it and i2 are movable along members l0and il. respectively so 2l and conse quently its resonant frequency maybe varied."

thereby.

The cathode is heated through lead I 6 from potential source I1. Thegrid electrode 3 is maintained at a potential near that oi the cathodeby lead I8 connecting to either potential source Il or I9; the plateelectrode 5 is maintained at a potential near that of the cathode bymeans of lead 20 connecting to either potential source Il or I9; and thegrid electrode 4 is maintained at a potential positive with respect tothe cathode and the other electrodes by means of lead 2| connecting topotential source I 8.

In operation, electrons emitted from the cathde 2 proceed in thedirection of the plate electrode under the influence of the gridelectrode 4. Upon passing through vthe grid electrode 4 the electronscome under the inuence of the high frequency neld associated with theresonator 21 and impressed upon the space between the grid 4 and plate5. Depending upon the phase of this field at the time an electronentersit the velectron is accelerated or decelerated and consequently someelectrons are accelerated and gain energy from the iield while othersare decelerated and give up energy to the eld. The electrode potentialsare made such that the electron transit time between the grid electrode4 and the plate electrode 5 is approximately the period of one-halfcycle of the frequency to which the cavity resonator 21 is tuned andalso such that electrons which have gained energy and been acceleratedare able to pass on to the plate electrode 5 where they are collected,in spite of the retardation due to the low potential of that electrode,while electrons which have given up energy and so lost velocity arestopped before reaching the plate electrode 5 and return toward thecathode yielding still more energy to the high frequency field as theyagain traverse the space between the plate 5 and grid 4. During eachcycle therefore more energy is given to the high frequency field than istaken from it because the electrons which absorb energy traverse theneld only once while those which give energy to the field traverse itagain in the opposite direction and thus oscillations are maintained inthe cavity resonator. High frequency energy thus generated in theresonator 21 may be delivered to a load circuit in any suitable mannersuch as through the coupling probe 28 to load resistor 23. It isdesirable to dimension the tube so that the distance between grids 3 and4 approximately equals that between grid 4 and plate 5 so that electronsreturning toward the plate a second or third time will pass through thespace between 4 and 5 in the proper phase.'

With a tube operated in this manner and a condition of complete spacecharge in the region between the cathode 2 and grid .3, 24centimeteroscillations were obtained with a bias potential of 60 volts between thegrid 4 and the cathode 2 while 1li-centimeter oscillations were had witha bias potential o! 107 volts. The oscillations were easily obtainedwithout critical adjustment of the circuit and the frequency ofoperation was readily changed by varying the tuning of the cavityresonator and the bias potentials. The output of the device may bevaried by changing the biasing potential of the grid electrode 3 andconsequently the output may be modulated by applying the modulatingvoltage to that electrode. It may be noted that while this device isoperated with complete space charge between the cathode and the firstgrid electrode 3 the usual Barkhausen oscillator. where rather closecoupling exists between the various regions of the tube, does notoscillate very well when space charge exists near the cathode..

While extremely satisfactory performance is had with the arrangement ofFig. 1 it is apparent that half of the emission of the cathode,represented by the electrons which enter the high frequency iield at 'atime to absorb energy and vbe collected at the plate electrode 5, notonly do not contribute to the high frequency output but actually absorbhigh frequency energy. This situation is improved in the arrangement ofFig. 2 where means are provided whereby the electrons leave the vicinityof the grid 3 in groups and in the proper phase to send the groups intothe held of the high frequency output circuit in the space between theelectrodes 4 and 5 at the proper time to deliver energy to theoscillations. In this way the useless electrons which in the operationof Fig. 1 absorb energy from the high frequency circuit are eliminated.In Fig. 2 a cavity resonator 26 is connected .to the cathode 2 and thegrid electrode 3 in the same manner as the resonator 21 is connected tothe grid electrode 4 and the plate electrode 5. This resonator whenenergized impresses a high frequency voltage between the cathode 2 andthe grid electrode 3 and the biasing potentials are adjusted so thatelectrons from the cathode pass the grid 3 and on to grid 4 only duringthe half cycles of the impressed high frequency voltage when the grid 3is made positive with respect to the cathode 2. The resonator 26 isbounded by members 3, 23, 1, 8. 9, 6, 22 and 2. Members 8 and 9 arespaced to provide direct current insulation between the cathode 2 andgrid electrode 3 land are movable along the coaxial members 6 and 1 tochange the size and tuning of the resonator. As between members I2 andI3 there is suicient capacitance between members 8 and 9 to effectivelyclose the resonator for high frequencies. 'I'he conducting sleeve memberI4 which is insulated for direct current .from electrodes 3 and 4 by aninsulating sleeve the field spaces of the resonators to coupletherewith. The flanges 33 and 35 with the insulating spacer 34 providedirect current insulation between the electrodes 3 and 4 and at the sametime provide a high frequency connection between the sections 3i and 32of the outer conductor of the coaxial line. The length of the line mustbe made such that the energy is introduced into the resonator 28 in suchphase relation to the energy in resonator 21 that a maximum number ofelectrons in each group released by the grid electrode 3 enters thespace between electrodes 4 and 5 in the proper phase to give up maximumenergy to the resonator 21. Ordinarily this condition is indicated bymaximum high frequency output of the device. It will vbe seen that inFig. 2 the cathode is heated and the various electrodes are biased bymeans .ofthe potential sources I1 and I9 generally the same as in Fig. 1and that a load resistance 23 is coupled to the resonator 21 in the samemanner in Figs. 1 and 2.

Tests of a circuit according to Fig. 2 showed a high frequency outputapproximately twice that of the Fig. 1 arrangement indicating theeffectiveness of the high frequency control of the electron stream inincreasing the output and ei'clency.

Fig. 3 illustrates a modification of Fig.. 2 in which the feedbackconnection is dispensed with and the relative biasing potentials arechanged to alter the over-all mode of operation. With-the exception thatthe feedback circuit is eliminated the electrodes and the high frequencyresonator circuits are arranged the same as in Fig. 2. The electrodebiasing potentials, however, are different inFig. 3 than in Fig. 2, thegrid 3 and plate 5 being made positive with respect to the cathode whilegrid 4 is made approximately the same potential as the cathode. In thisarrangement high frequency oscillations are generated in the resonator26 in much the same manner as in the resonator 21 in the Fig. 1arrangement. Electrons which cross the space between the cathode 2 andthe grid 3 in the phase of the high frequency iield associated with theresonator 26 to give up energy to it and on that account are retardedwill not be able to overcome the retardation of the low potentialelectrode 4 and so will be returned toward the cathode and will againtraverse the space between the cathode 2 and the grid 3, in the oppositedirection, again giving energy to the resonator 26. The result of thismultiple crossing of the space between 2 and 3 by the energy givingelectrons is a preponderance of energy giving traversals of the spacewhich sustains the oscillations in the resonator 26 in the and means forcausing a flow of electrons alongat least a portion of a path extendingbetween the manner the oscillations are sustained in resonator 21 ofFig. 1. However, the oscillations generated in resonator 26 are notcoupled directly to the load circuit as were the oscillations generatedin resonator 21 of Fig. 1. The electrons which cross the space betweenthe cathode 2 and the grid 3 in the 'phase of the high frequency fieldto absorb energy from it are accelerated so that they are able toovercome the retardation of the low po- -tential electrode 4 and passthat electrode, after which they are accelerated and collected by theplate electrode 5. These electrons reach electrode and cross the spacebetween 4 and the plate electrode 5 in groups at the frequency of theoscillations in the resonator 26 and, therefore, generate energy at thatfrequency in resonator 21. Resonator 21 then is the resonant outputcircuit and it is excited by the groups of electrons which have beenaccelerated during traversal of the space between electrodes 2 and 3 sothat they arel able to pass electrode Il. 'I'he load circuit 29 iscoupled to the resonator 21 by means of the probe 28 as in the otherfigures.

In the arrangement of Fig. 3 the load is coupled to the frequencydetermining circuit (resonator f ing an electron discharge tubecontaining at least i four planar electrodes namely an electron emittingcathode, a plate electrode, a iirst grid electrode between the cathodeand the plate electrode and a second grid electrode between the iirstgrid electrode and the plate electrode, a high frequency circuitcomprising a substantially closed electrical cathode and the plateelectrode comprising a source of velectric potential connected to eachof the said electrodes and to at least one other said electrodewherebysuitable potential diierences are maintained between the variouselectrodes, the potential differences being such that the potential ofthe second grid electrode is maintained positive with respect to thecathode and to the other two electrodes and also such that the electrontransit time between the second grid electrode and the plate. electrodeis substantially the period of one-half cycle of the resonant frequencyof the second high frequency circuit. a

2. A high frequency oscillator comprising an electron discharge tubecontaining at least four planar electrodes namely an electron emittingcathode, a plate electrode, a first grid electrode between the cathodeand the plate electrode and a second grid electrode between the firstgrid electrode and the plate electrode, a high frequency circuitcomprising a substantially closed electrical resonator system comprisingcoaxial conducting members external to the said electron discharge tubeand which includes the electron emitting surface of the cathode and thefirst grid electrode, a second high frequency circuit comprising a.substantially closed electrical resonator system comprising coaxialconducting members external to the said electron discharge tube andwhich includes the platel electrode and the second grid electrode, meansfor connecting the two high frequency circuits in feedback relation andmeans for causing a ilow of electrons along at least a portion of a pathextending between the cathode and the plate electrode comprising asource of electric potential connected to each of the said electrodesand to at least one other said electrode whereby suitable potentialdifferences are maintained between the various electrodes, the potentialdifferences being such that the potential of the second grid electrodeis maintained positive with respect to the cathode and to the other twoelectrodes and also such that the electron transit vtime between thesecond grid electrode and the plate electrode is substantially equal tothe period of one-half cycle of the resonant frequency of the secondhigh frequency circuit.

3. A high frequency oscillator circuit compris,- ing an electrondischarge tube containing at least four planar electrodes namely anelectron emitting cathode, a plate electrode, a iirst grid electrodebetween the cathode and the plate electrode and a second grid electrodelocated substantially midway between the iirst grid electrode and theplate electrode, a high frequency circuit comprising a substantiallyclosed electrical resonator system comprising coaxial conducting membersexternal to the said electron discharge tube and which includes theelectron emitting surface of the cathode and the iirst grid electrode, asecond high frequency circuit comprising a substantially closedelectrical resonator system comprising coaxial conducting membersexternal to the electron discharge tube and which includes the plateelecv 7 trode and the second grid electrode and means for causing a flowof'electrons along at least a assedic? portion of a path extendingbetween the cathode.'

andthe plate electrode comprising asource of electric potentialconnectedV to each of the said electrodes and to at least one other saidelectrode whereby suitable potential differences are maintained betweenthe various electrodes, the potential differences being such that thepotential of the second` grid electrode is maintained positive withrespect to the cathode and to the other two electrodes and also suchthat the electron transit time between the second grid electrode and theplate electrode is substantially the period of oneihaif cycle of theresonant frequency oi;I the second high frequency circuit.

4. A high' frequency oscillator comprising an electron discharge tubehaving a planar cathode,

a planar, anode and at least one Planar electron permeable electrodelocated therebetween such that an electron stream passing from thecathode to the anode traverses each of the spaces between the'variouselectrodes, a cavity resonator comprising coaxial conducting membersexternal to i the said electron discharge tube and connected for highfrequencies to two of the said electrodes other than the cathode whichare adjacent to each other such that when theresonator is energized aportion of its alternating electric field is impressed upon the spacebetween the electrodes connected to it, means for varying the resonatorfrequency comprising members slidable longitudinally between the saidcoaxial conducting mem-` bers and means comprising a source of electricpotential connected to each of the said electrodes and toat least oneother said electrode for producing a stream of electrons from'thecathode to the anode and for establishing ixed potential differencesbetween the electrodes, the potential dif.. ferences being su'ch that ofthe two electrodes connected to the resonator the one located nearer thecathode is the .more positive with respect to the cathode and, further,the potential dlierences and the distances between the electrodes beingv and later encounter y 8 an electrode substantially negative withrespect to the said permeable-positive electrode whereby'electrons arereversed and prevented from reaching the anode.

6. A high frequency oscillator circuit comprising an electron dischargetube 'containing at least four planar electrodes namely an electron emitting cathode, a plate electrode. a iirst grid electrode between thecathode and the plate electrode and a second grid electrode between thefirst grid electrode and the plate electrode, a high frequency circuitcomprising a substantially closed electrical resonator system comprisingcoaxial conducting members external to the said electron discharge tubeand which includes the electron emitting surface of the cathode and therst grid electrode, a second high frequency circuit comprising asubstantiallyclosed electrical resonator system comprising -coaxialconducting members external to the electron discharge tube and whichincludes the plate electrode and the second grid electrode,

. frequency control means comprising a movable member included with eachof the said resonator` systems whereby the resonant frequency of each ofthe systems'may be readily varied and means for causing a fflow ofelectrons along at least a portion of a path extending between thecathode and the plate electrode comprising a source of electricpotentialconnected to each of the said t electrodes and also such thatthe electrontransit tron path terminating electrodes termed cathode andanode and at least one planar electron peran electron stream passingfrom the cathode to the anode traverses each of the spaces between thevarious electrodes, a cavity resonator comprising coaxial conductingmembers external to the said electron discharge tube connected to two ofthe said electrodes which are adjacent to each other and of which one isan electron path terminating electrode such that when the resonator isenergized a portion of its alternating electric held is impressed uponthe space between the electrodes connected to it, frequency controlmeans comprising a movable member included with said resonator and meanscomprising a source oi' electric potential connected to each of the saidelectrodes and to at least one other said .electrode for producing astream oi electrons from the cathode to the anode and for establishing.anode encounter an electron permeable electrode meable electrodelocated therebetween such that potential diierences between theelectrodes, the

time between the second grid electrode and the plate electrode( issubstantially the period of one.

half cycle of theresonant frequency of the second velectron dischargetube having two planar electron path terminating electrodes termedcathode and anode and at least one planar electron permeable electrodelocated therebetween such that an electron stream passing from 'thecathode to the anode traverses each of the spaces between the variouselectrodes, a cavity Iresonator comprislng coaxial conducting membersexternal tothe said electron discharge tube connected to two of the saidelectrodes which are adjacent to-each other and of which one is anelectron path terminating electrode such that when the resonator isenergized a portion of its alternating electric fleld is impressed uponthe space between the electrodes connected to it, frequency controlmeans comprising a movable member included with said resonator and meanscomprising a source of electric potential connected to each of saidelectrodes and to at least one other said electrode for producing a.stream of electrons from the cathode toward the anode and forestablishing potential differences between the electrodes, the potentialdiiferences being such that. electrons traversing the path between thecathode and anode encounter an electron permeable electrodesubstantially positive with respect to the cathode and later encounteran electrode substantiallyv continue along the path to the anode.

l 8. A high frequency oscillator circuit comprising an electrondischarge tube containing at least substantially positive with respectto the cathode 7|, four planar electrodes namely anelectron e1nit-L tingcathode, alzplate electrode, a first vgrid electrode between the cathodeand the plate electrode and a second grid electrode locatedsubstantially midway between the first grid electrode and the plateelectrode, a high frequency circuit comprising a substantially closedelectrical resonator system comprising conducting members external to.

the said electron discharge tube which includes the electronemittingsurface of the cathode and the first grid electrode, a second highfrequency circuit comprising a substantially closed electrical resonatorsystem which includes the' plate electrode and the second grid'electrode, frequency 1 control means comprising a movable memberincluded with each of the said resonator systems whereby the resonantfrequency of each of the systems may be readily varied and means forcausing a flow of electrons along at least a portion of a path extendingbetween the cathode and the plate electrode comprising a source ofelectric potential connected to each of the said electrodes and to atleast one other said electrode whereby suitable potential differencesare maintained between the various electrodes, the potential differencesbeing such that the potential of the second grid electrode is maintainedpositive with respect to the cathode and to the other two electrodes andalso such that the electron transit time between the second gridelectrode and the plate electrode is substantially the period ofone-half cycle of the resonant frequency of the second high frequencycircuit.

9. A high frequency oscillator comprising an electron discharge tubecontaining at least four planar electrodes namely an electron emittingcathode, a plate electrode, a first grid electrode between the cathodeand the plate electrode, arid a second grid electrode between the firstgrid electrode and the plate electrode, a high frequency circuitcomprisinga. substantially closed electrical resonator system comprisingcoaxial conducting members external to the said electron discharge tubewhich includes the plate electrode and the second grid electrode, meansfor causing a flow of electrons along at least a portion of a pathextending between the cathode and the plate electrode comprising asource of electric potential connected to each of the said electrodesand to at least one other said electrode wherebyI suitable potentialdifferences are maintained between the various electrodes, the potentialdifferences being such that the potential of the second grid electrodeis maintained positive with respect to the cathode, and to the other twoelectrodes and means comprising the first-grid electrode for controllingat low frequency the high frequency output of the oscillator.

10. A high frequency oscillator comprising an electron discharge tubecontaining an electron emitting cathode, a plate electrode, a rst gridthe electron emitting surface of the cathode and v the first gridelectrode, a. second high frequency circuit comprising a substantiallyclosed electrical resonator system which includes the plate electrodeand the second grid electrode, means comprising a movable memberincluded with each of the said resonator systems for varying theresonant frequency of the two resonant systems and electric potentialsources connected to the cathode and other said electrodes formaintaining suitable assess? Potential differences therebetween and 'forcausing a ow of electrons along at least a portion of a path extendingbetween the cathode and the plate electrode, the said potentialdifferences being such that the first grid electrode and the plateelectrode are maintained at potentials positive with respect to thecathode and the secondgrid electrode is maintained at a potentialnegative with respect to the first grid electrode and the plateelectrode. v

11. A high frequency oscillator comprising an electron discharge tubehaving two planar electron path terminating electrodes, one being acathode and one an anode, and at least one planar electron permeableelectrode located therebetween such that an electron stream passing fromthe cathode to the anode traverses each of the spaces between thevarious electrodes'. a cavity resonator comprising coaxial conductingmembers external to the said discharge tube connected to two of the saidelectrodes which are adjacent to each other and of which one is anelectron path terminating electrode such that when the resonator isencrlgized a portion of its alternating electric field is impressed uponthe space between the electrodes connected to it, means for varying theresonator frequency comprising members slidable longitudinally betweenthe said coaxial conducting members, `electric potential sourcesconnected to the said electrodes for producing a stream of electronsfrom the cathode to the anode and for establishing potential differencesbetween the electrodesl the potential differences being such thatelectrons traversing the path from the cathode toward the anodeencounter an electron permeable electrode substantially positive withrespect to the cathode and later encounter an electrode substantiallynegative with respect to the said permeable positive electrode,

12. A high frequency oscillator comprising an electron discharge tubecontaining at least four planar electrodes namely an electron emittingcathode, a plate electrode, a rst grid electrode between the cathode andthe plate electrode and a second grid electrode between the first gridelectrode and the plate electrode, a high frequency circuit comprising asubstantially closed electrical resonator system comprising conductingmembers preponderantly external to the said electron discharge tube andwhich includes the electron emitting surface of the cathode and thefirst grid electrode, a second high frequency circuit comprising asubstantially closed electrical resonator system comprising conductingmembers preponderantly external to the electron discharge tube and whichincludes the plate electrode and the second grid electrode, frequencycontrol means comprising a movable member included with each of the saidresonator systems whereby the resonant frequency of each of the systemsmay be readily varied and means for causing a flow of electrons along atleast a portion of a path extending between the cathode and the plateelectrode comprising a source of electric potential connected to each ofthe said electrodes and to at least one other said electrode wherebysuitable potential differences are maintained between the variouselectrodes, the potential differences being such that the potential ofthe second grid electrode is maintained positive with respect to thecathode and to the other two electrodes.

13. A device according to claim 5 in which the said resonator includesthe said anode.

14. A device according to claim 5 in which the said potentialdifferences and the distances between fhe electrodes are suchiliatflie.*letxon l transit time between the electrodes connected to theresonator is s. period substantially equal to the electric eld.

MORQN,

Name Date v Linder -1-1.--- Mar. 23. 1943 Southworth Apr. 11, 1939Chev1gny,y--.-..-..-.'.. June 20, 1944 e Dallenbach Aug. 30, 1938 VarianJuly 29, 1941 Morton Mar. 31. 1942 -'Linder .........;.----e.. Aug. 18.1942 Aus. 18, 1942 *K

